One thing I learned from watching the Timberwolves flounder for the last decade is that this can be a no-win situation. They had Chauncey Billups for cheap as a back-up right before he was ready to break out, but chose instead to stick with their vet starter (Brandon) and replace Chauncey with another cheap, unproven FA (Troy Hudson). Then, after Hudson had a good playoff run (and still smarting from getting burned by Chauncey), the Wolves gave Hudson the long mid-level contract and it blew up in their face. They offered similar deals to guys like Marko Jaric, Mike James, and Trenton Hassell and had it blow up in their faces when they proved to be back-up caliber more-so than starting caliber. The contracts themselves, some of which seemed reasonable at the time, became albatrosses.
My inclination would be to sign Posey for the good karma, and the fact that he seems to fit so well on this team. But my mind looks at Minnesota's history, and the lesson there was that you only give these long mid-level contracts to starting caliber players with upside. Posey isn't that. So while I'll probably be happy if I hear that Posey has been re-signed by the Celtics, I couldn't at all fault the logic of not overspending on him in order to keep needed financial flexibility moving forward. With the starting 5 locked up the foundation is good here for at least the next few years, and Posey is more of a luxury. It is sound logic to not tie the team up financially for a luxury.